Introducing MNT Reform Next https://mntre.com/media/reform_md/2024-09-09-introducing-mnt-reform-next.html
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Riley S. Faelanreplied to Riley S. Faelan last edited by
@gkrnours Nm, https://source.mnt.re/reform/reform-next/-/tree/main/nref-motherboard?ref_type=heads seems to be where the drafts are. But there's no PDF yet, and my KiCad is just too old to reject the files, so I can't take a look today.
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Riley S. Faelanreplied to Riley S. Faelan last edited by [email protected]
@gkrnours This is the datasheet for the charge controller chip on the new model: https://www.ti.com/lit/ds/symlink/bq25756.pdf. You can see the registers from page 39 onwards.
My hunch is, looking at them, that this charge controller may well be software-adjustable to NaIon battery chemistry.
For a somewhat better heuristic, if you can see the schematic, check out how the DIP switch between LiFePO4 and LiIon works. If it notifies the system management chip, which then loads the charge parameters into the charge controller's registers over I2C, things are good. If it instead switches resistors on or off at some sort of voltage sense pathway, then more resistor-switching might be necessary, or preferable, to switch the system over to NaIon.
Oh! And if you can find the source code for the Reform Next's system management chip, the presence or lack of code for loading the charge controller's charging parameter registers should also be readily visible there.
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@mntmn The catch is, resistors are hardware pieces. If the feedback control is implemented by a pair of resistors translating the battery voltage to a fixed-threshold voltage, then switching over to a future battery tech may require switching out the resistor, and doing it on a laptop's motherboard can be a bit cumbersome, creating a significant barrier for users who might want to switch to NaIon batteries down the line. If such resistors were on a separate sub-board plugged into the motherboard, then switching it/them would be a lot easier — when the time cames, one can just replace the sub-board. Or maybe, a bit more heretically, through-hole resistors could be used, plugged into a header, allowing for tool-less replacement. (I suspect such a not-really-standard-anymore connector would create manufacturing inconveniences, though.)
It might not actually be an issue if the charge controller doesn't interpret the feedback voltage at fixed thresholds, but at software-controlled thresholds, so different values could be used according to the applicable battery chemistry. I don't know for sure whether bq25756 supports that; the datasheet gives me hope that this might be the case, but I haven't read it in depth yet.
Or, as a third alternative, considering that battery techs don't change all that often, and the charging characteristics of NaIon batteries aren't exactly a dark mystery, maybe it would be feasible to just make sure that the system is ready for NaIon batteries as a third battery tech, next to LiIon and LiFePO4, to begin with?
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@gkrnours And placed a bit apart from the other parts, to allow for inexperienced people working with large tools and no microscope.
In the olden days, potentiometers would have been used for this, allowing the resistance to be smoothly regulated using a screwdriver. But in the context of charging a battery, that might not be the ideal way.